Method to increase solar cell performance

To fly in the dark and evade prey, moths' eyes are almost non-reflective. This feature has been exploited and developed by scientists to become an anti-reflective film coated with solar cells. Now, a research team at the University of North Carolina has continued to improve the technology to increase battery performance as high as possible.

Professor Chih-Hao Chang and his colleagues developed a new film, designed to minimize thin film interference in solar panels.Thin-film interference is a phenomenon that occurs when incident light waves are reflected by the upper and lower layers of a thin plate interfering with each other to create a new wave. According to the theory, a thin film is a layer of material with a thinness from semi-nanometer to micron. When light hits the surface of a thin film, it can simultaneously reflect at the top surface and propagate downwards. When exposed to the underside, light continues to pass or is reflected. The light reflected from the upper and lower surfaces will interfere and the interference that enhances or eliminates between the two light waves depends on the difference in their phases.

This difference is based on the film's thinness, the film's refractive index and the angle of incidence of the initial light on the film. The light resulting from the interference can appear as bright and dark bands or colors depending on the incoming light source. An example we often see about thin film interference is rainbow-colored streaks of color on a slick or soap bubble. The oil floats on the surface of the water, light reflects off the surface of the oil, but part of the light also penetrates this surface and reflects from the water layer below. Because the two sources reflect light differently on optical properties, they interfere with each other and create a rainbow effect.

A similar phenomenon may occur when thin films are placed on each other. In the case of photovoltaic batteries, they are made up of many thin films stacked on top of each other and light often loses between film layers where interference occurs.

In order to overcome this problem, Chang's team developed films that incorporate conical nanostructures, similar to the convex structure in moth eyes. When appearing on the surface of a film, these structures can penetrate the underside of another film above, like Lego bricks. As a result, the phenomenon of interference between the plates hardly happens. The process continues to repeat with multiple overlapping films.

According to scientists, the amount of light reflected by one of the surfaces with nanostructures is only 1/100 of the surface of conventional solar panels. Currently, they plan to apply the technology on a solar device and search for commercial applications.

Chang's work with colleagues from North Carolina University has been published in the journal Nanotechnology in the past week.